fix: Correction dépendances circulaires

Back-End/Common/models.py

@@ -0,0 +1,13 @@
+from django.db import models
+
+class StudentCompetency(models.Model):
+    student = models.ForeignKey('Subscriptions.Student', on_delete=models.CASCADE, related_name='competency_scores')
+    competency = models.ForeignKey('School.Competency', on_delete=models.CASCADE, related_name='student_scores')
+    score = models.DecimalField(max_digits=5, decimal_places=2, null=True, blank=True)
+    comment = models.TextField(blank=True, null=True)
+
+    class Meta:
+        unique_together = ('student', 'competency')
+
+    def __str__(self):
+        return f"{self.student} - {self.competency.name} - Score: {self.score}"